The greenhouse gas emission reduction targets for developed countries were set in the Conference of the Parties of the UN Framework Convention on Climate Change in 1997. Thus, reduction in emission of CO2 gas, whose emission to the air is the largest among greenhouse gases, is required. Meanwhile, a gas separation membrane that selectively separates a target gas from a gas mixture is known. Especially, a polymeric gas separation membrane has excellent permeability and processability, and is expected to be employed for the use in separating CO2 gas, which is emitted in a large amount in thermal power stations, factories, and the like. For example, Patent Document 1 describes that gas separation membranes formed from cellulose acetate have been industrially widely used.
Furthermore, Patent Document 2 discloses a gas separation membrane including a gas separation layer including a polyimide compound including a particular diamine, represented by 3,5-dinitro-2,4,6-trimethylbenzenesulfonamide, to provide a gas separation membrane achieving both excellent gas permeability and excellent gas separation selectivity, exhibiting excellent gas permeability and excellent gas separation selectivity even under high pressure conditions, and having a gas separation layer that is less likely to be affected by impurities, such as toluene, present in natural gas.